Public schools accountable?

Over and over again I've heard an ad telling me that private schools are not accountable. Then why are so many people signing up to get into private schools? Certainly there's accountability  accountability to those who pay the bill. Yet in the public school system, millions of dollars have been allotted by the Legislature over the past several years to make class sizes smaller. That has never happened. Somehow, the districts managed to spend that money on other things. Do we call this accountability?